Effects of Imaging on Signal‐to‐noise Ratio, With Varying Signal Conditions

Abstract

Perky's finding, that an observer confuses his internal imagery with a normally supraliminal stimulus, has been reinterpreted in signal detection language. Two experiments compared a task where the subject was asked concurrently to image items and discriminate signals from noise to a task where the subject only discriminated signals. The subject's criterion was slightly higher in the imaging task and sensitivity (d′) was significantly lower, whether the imaging task was given before or after the discrimination task. As d′ measures signal‐to‐noise ratio, it was suggested that imaging alters d′ because it is a source of neural activity. This activity can be conceptualized as internal noise or as another signal. For some subjects, stimuli were gradually brightened; for others, they were presented briefly at full brightness. Mode of onset did not affect d′, rather d′ depended on brightness summed over time.

Unmasking the Perky Effect: Spatial Extent of Image Interference on Visual Acuity

“…As expected, the results show a clear Perky effect, as imagined lines reduced acuity. The reduction is 17.6% when the imagined lines are “ON” the target, in line with Segal and Fusella (1970), Reeves (1980), and Craver-Lemley and Reeves (1987, 1992). The Perky effect was attenuated if the image was shifted off target, in the present research from 17.6 to 6.3% (i.e., baseline No Image – image OFF), also in line with Craver-Lemley and Reeves (1987).…”

“…In our earlier work, we argued in favor of analogous spatial behavior but against substitutability (Arterberry et al, 2002), based on empirical findings concerning the so-called Perky effect, in which visual images, analogous to real masking stimuli, can suppress perception of real visual targets (as discovered by Perky, 1910). The Perky effect is ubiquitous in studies of percept-image interactions, with the imagined stimulus depressing sensitivity to briefly flashed visual targets by 15% or better (0.8 d′ units or more; Segal and Fusella, 1970; Craver-Lemley and Reeves, 1987, 1992; Ishai and Sagi, 1997). In the Perky experiments, the experimenter requested that the subject project his or her visual image in the location of the visual target.…”

“…Moreover, the Perky effect does not stem from demand characteristics; participants told that imagery aided perception produced as great a Perky effect as those told it would hinder perception (Craver-Lemley and Reeves, 1987, Experiments 1a and 1b). Other experiments have ruled out mere distraction, the notion that having any image would add a load to the cognitive system and thus lower visual performance, as auditory images have virtually no effect on visual target (Craver-Lemley and Reeves, 1992; although they do on auditory ones: Segal and Fusella, 1970), visual images located far away from the visual target have almost no effect (Craver-Lemley and Reeves, 1987; Craver-Lemley and Arterberry, 2001), and diverting attention to a distracting light does not increase the interference (Craver-Lemley and Reeves, 1992). Thus we have used the Perky effect as a test-bed for discovering whether images and real visual stimuli have the same functional properties.…”

Crossmodal Constraints on Human Perceptual Awareness: Auditory Semantic Modulation of Binocular Rivalry

“…Note, however, that Pearson et al (2008) also reported that when the background was 100% illuminated (i.e., a white background, as in the present study), their participants performed similarly under the conditions of viewing passively and generating a mental image. Besides, Segal and Fusella’s (1969, 1970) early studies demonstrate that a person’s sensitivity to detect a visual (or auditory) target was lowered when he/she imaged that stimulus in the same sensory modality. Such modality-specific suppression during mental image generation has recently been observed in primary sensory areas in humans (i.e., visual and auditory cortices, see Daselaar et al, 2010).…”

Feels like the real thing: Imagery is both more realistic and emotional than verbal thought

“…First, there is evidence of competition between mental imagery and perceptual processing when they share the same sensory modality. Holding a visual image selectively interferes with the detection of a faint visual signal, and, likewise, auditory images interfere with the detection of auditory stimuli (Segal & Fusella, 1969). The reverse relationship also holds: judged vividness of visual images is reduced by simultaneous performance of a visuospatial task, and auditory image vividness is decreased by counting aloud (Baddeley & Andrade, 2000).…”